<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
    <style>
        *{padding:0;margin: 0;}
        .row:after{
            content: "";
            display: table;
            clear: both;
        }
      ul{
          list-style: none;
      }
      ul li{
          float: left;
      }
      .main-frame{
          font-size: 15px;
          background: pink;
          line-height: 20px;
      }
      .main-frame li{
          border: 1px solid #333;
          width:50px;
          text-align: center;
          display: block;
      }
      .shangla{
          position: relative;
      }
      .xiala{
        position: absolute;
        width:50px;
        display: none;
      }
      .xiala a{
          color:blue;
          text-decoration: none;
          display: block;
      }
      .shangla:hover .xiala{
          display: block;
      }
    </style>
</head>
<body>
    
        <ul class="main-frame row">
            <li class="shangla">一号
                <div class="xiala">
                    <a href="">小一号</a>
                    <a href="">小二号</a>
                </div>
            </li>
            
            <li>二号</li>
            <li>三号</li>
        </ul>
  
</body>
</html>